For the past several years, the Environmental Protection Agency has been proposing regulations which would limit the amount of fuel vapor released into the atmosphere during the refueling of a motor vehicle. During refueling, the incoming fuel must displace fuel vapor from the head space in the fuel tank and this displaced vapor is vented through the filler pipe into the atmosphere. Air pollution and safety problems resulting from this situation are obvious.
One approach to this problem, presently in use in California, has been to equip the fuel dispensing pumps at service stations with a vapor recovery system which collects fuel vapor discharged from the fuel tank filler pipe during the refueling operation and transfers the vapor to a storage tank. The primary drawbacks of this system are the substantial expense involved in equipping each individual fuel pump with the necessary components of the system and the present lack of a safe and economically practical method for disposing of the vast quantities of fuel vapor collected by the system.
In recent years, on board (vehicle carried) fuel vapor recovery and storage systems have been developed in which the head space in the vehicle fuel tank is vented to atmosphere through a charcoal filled vapor canister and fuel vapor is withdrawn from the canister into the engine intake manifold for mixture and combustion with the normal fuel charge. Because the fuel tank head space must be vented to enable fuel to be withdrawn from the tank during vehicle operation, this system addresses the problem of the discharge of fuel vapor through the atmospheric vent to the tank when ambient pressure and temperature conditions are such that vapor pressure within the fuel tank exceeds atmospheric pressure.
In the typical system of this type, the canister outlet is connected to the intake manifold of the vehicle engine through a normally closed purge valve. A computer which monitors various vehicle operating conditions controls opening and closing of the purge valve to assure that the fuel mixture established by the carburetor is not overly enriched by the addition of fuel vapor from the canister to the mixture. Thus, with the opening and closing of the purge valve between the canister and intake manifold, the canister is intermittently subjected to intake manifold vacuum. The atmospheric vent of the canister is relatively restricted to enable the development of a pressure differential withdrawing vapor from the canister when it is connected to the intake manifold. The flow and storage capacities of such a system, which will be referred to as a "running vapor recovery system", are totally inadequate to cope with the massive surge of fuel vapor displaced from the fuel tank during a refueling operation.
The present invention is directed to an on board refueling vapor recovery system which may be operated in parallel with the running vapor recovery system described above to prevent the discharge of the relatively large quantities of fuel vapor displaced from the fuel tank during refueling into the atmosphere and to store fuel vapors so recovered for combustion at a controlled rate by the vehicle engine.